1) Field of the invention
This invention relates to a process for improved homopolymerization or copolymerization of vinyl chloride; in particular, to a process for preventing adhesion of polymer to an inner wall of a polymerization apparatus such as a polymerization tank and to a polymer adhesion inhibitor therefor.
2) Prior Art
When vinyl chloride is subjected to homopolymerization or copolymerization with a monomer copolymerizable with vinyl chloride, or graft polymerization (hereinafter, collectively referred to as "polymerization"), polymer may adhere to parts of an apparatus such as an inner wall of a polymerization tank, a reflux condenser, a stirring blade, a baffle and various types of pipe connections, in contact with monomer(s) during a polymerization process, causing problems such as reduction of coolability of the polymerization tank and degradation in quality of the homopolymer or copolymer of vinyl chloride (hereinafter, referred to as "the product") due to contamination with peeled polymer which has been adhered to some surface.
It is therefore usual that after every polymerization process, the inside of the polymerization tank is cleaned prior to a next polymerization process, which requires an enormous amount of labor and time, leading to reduction in productivity rate of the polymerization tank or increase in the cost for the product.
To solve the problem, there have been proposed processes for preventing a polymer adhesion to an inner wall of a polymerization tank and/or other parts by applying some agent; for example, JP-B 61-843 (U.S. Pat. No. 4,355,141) has disclosed a process comprising application of a cocondensation product of resol with a nitrogen-containing compound such as nitrophenols, nitrobenzoic acids, aminophenols and aminobenzoic acids, and JP-A(KOHYO) 2-500845 (PCT-US-88-02462, WO-89-00993) and JP-A (KOHYO) 5-501892 (PCT-US-90-05829, WO-91-06576) have proposed processes comprising application of a condensation product of phenothiazine with an aldehyde.
However, the process according to JP-B 61-843 does not sufficiently prevent scale adhesion, and a more effective method is desired. For the processes described in JP-A 2-500845 and JP-A 5-501892, since the adhesion inhibitor used can be dissolved only in an organic solvent, a particular type of organic solvent should be used as a solvent for a coating liquid, making the apparatus and/or the operation more complex in the light of safety in handling and due to need for recovery of the solvent from the polymerization system. Furthermore, there are practical problems; for example, inadequate recovery of the solvent adversely affects the quality of the product.
3) Object of the Invention
Thus we have investigated for making it possible to quite effectively prevent polymer adhesion in, e.g., a polymerization tank, in polymerization of a vinyl chloride monomer, without affecting a polymerization rate or physical properties of the product; to apply an adhesion inhibitor as a coating liquid containing no or a very small amount of organic solvents; to eliminate the need for removing adhered polymer after every polymerization process; and to realize closed polymerization in which a manhole should not be opened for every polymerization process.